DETROIT (Reuters) – U.S. presidential hopeful Donald Trump sought to regain campaign momentum as four states including Michigan voted on Tuesday, after a barrage of attacks from fellow Republicans and a tightened race created an opening for those seeking to block him.

The Republican front-runner split four contests on Saturday with conservative rival Ted Cruz, who positioned himself as the prime alternative to Trump in the race for the party’s nomination in the Nov. 8 election.

Michigan is the biggest prize up for grabs in Tuesday’s contests. Most opinion polls show the New York real estate magnate hanging on to a solid double-digit lead there over Cruz, a U.S. senator from Texas, and Ohio Governor John Kasich, who has climbed in some opinion polls in the Midwestern state.

While Kasich is in last place in the number of delegates amassed, which are needed to clinch the nomination at the party’s July convention, a strong showing for him in the state could complicate the math for any one anti-Trump candidate.

“The whole world’s watching what’s going to happen in Michigan tonight,” Kasich, 63, told a rally in Lansing.

U.S. Senator Marco Rubio of Florida is the favorite of a Republican establishment alarmed by Trump’s controversial proposals and crude style and anxious about Cruz’s uncompromising conservatism. But Rubio, 44, lags behind and may need a win in his home state next week to keep his campaign alive.

Trump, 69, faced a week of blistering attacks from the party’s establishment that ended with a mixed showing in Saturday’s contests in Louisiana, Kentucky, Kansas and Maine.

That encouraged some Republican leaders and donors who are trying to block him from a clear shot at the party nomination.

FLORIDA ADS

Anti-Trump Super PACS have spent millions in advertisements designed to attack Trump’s character in Florida, a state Rubio calls home and Trump calls a second home. Florida’s 99 delegates are awarded on a winner-take-all basis.

“They are trying and they’re spending millions of dollars but I have a tremendous following,” Trump said Tuesday on Fox News, taking credit for the massive Republican voter turnout in the 2016 campaign. “That’s what’s happening – there’s life now in the Republican Party,” he added.

Many mainstream Republicans have been offended by Trump’s statements on Muslims, immigrants and women and alarmed by his threats to international trade deals. Trump said on Tuesday he has not assembled a foreign policy team, despite having said he would have one in place by February, and dismissed criticism his statements would be harmful to U.S. interests.

Conservatives meeting in recent days at the Republican Governors Association retreat in Park City, Utah, and a think tank gathering in Sea Island, Georgia, believe Trump will be vulnerable to another blast of attacks before a big day of voting on March 15, the Washington Post reported.

Apple CEO Tim Cook, Google co-founder Larry Page and billionaire Philip Anschutz, as well as congressional leaders, were among those attending the Sea Island event, the American Enterprise Institute’s World Forum over the weekend, which was closed to media, the Huffington Post reported.

Tesla and Space-X entrepreneur Elon Musk told Reuters he gave a talk on technology innovation at the forum. He said he was an independent who believes “in supporting reasonable candidates that show wisdom in their actions, understanding that no one is perfect, and empathy for all.”

On Tuesday, Republicans and Democrats were also voting in Mississippi, and Republicans in Idaho and Hawaii were making their choices on a day when 150 Republican delegates and 166 Democratic delegates will be up for grabs.

But the focus was on the industrial battleground of Michigan, where Trump’s relentless anti-free trade rhetoric and promise to slap taxes on cars and parts shipped in from Mexico has resonated in a state that has lost tens of thousands of manufacturing and auto industry jobs.

In the Democratic race, Hillary Clinton, 68, has a solid lead in Michigan opinion polls over rival Bernie Sanders, 74, a U.S. senator from Vermont.

Big Michigan wins for Trump and Clinton would set them up for a potentially decisive day of voting on March 15 in Ohio, Florida, Illinois, Missouri and North Carolina.

Michigan was the state that spawned the term Reagan Democrats to refer to largely white, working-class voters who abandoned their party to vote Ronald Reagan into the White House in the 1980s.

Sal Isabella, a Dearborn insurance agent, said he was for Trump because he would make things happen.

“He’ll be like Reagan,” Isabella said. “He’ll make some big changes and we need big changes.”